1. Field of Invention
This invention is concerned with a passive object identification system and method and more particularly with such a system and method employing a radiometer and radiometry measurements respectively.
2. Description of the Prior Art
There are any number of systems for identifying tagged objects which operate by illuminating the tag with microwave energy and then receiving back from the tag a coded signal. The coded signal may be as simple as double the frequency of the illuminating signal as typically used in department stores to identify merchandise or to prevent merchandise from being stolen. Alternatively the coded signal may be some type of digital code uniquely identifying the tag and thus the target to which it is attached. Other radio frequency systems that utilize interrogators and cooperating transponders are also known. In a military environment, the use of illuminating electromagnetic radiation at any frequency is undesirable as the enemy can discover the source of the energy radiation and neutralize the source. Yet it is important to be able to distinguish a friendly vehicle from an enemy vehicle by other than visual means.